Synthesis, Structural Characterization, and Electrical Properties of (Sr_0.5Ca_0.5)(Ca_0.5Sb_0.5)O_3−δ Double Perovskites

Abstract

Double perovskites which exhibit 1:2 B-site ordering are under focus because of their interesting structure-property relationships and high chemical versatility. Perovskites with a big cation, such as Sr 2þ or Ca 2þ , occupying the octahedral B site are very scarce because the calculated Goldschmidt tolerance factor becomes quite small as these types of cations usually occupy the A-site. This work describes the synthesis and structural and microstructural characterization of a new calcium and strontium antimoniate which shows face-centered cubic symmetry and a rock-salt ordered distribution of Sb 5þ and Sr 2þ . The ordered-cation distribution occurs due to the differences in both the ionic sizes and the bonding character of the two B-site cations. As a consequence of the cation stoichiometry of the title phase and assuming a pentavalent state for Sb, a large concentration of oxygen vacancies are created (y ∼ 0.25). Diffraction studies reveal that these vacancies tend to arrange in a short-ordered way and are related to oxygen ionic conductivity (10 -3 S/cm at 700 °C) which makes these materials potential candidates to be used as electrolytes in solid oxide fuel cells (SOFC).

Phase Chemistry in the Ca‐Mn‐Sb‐O System at 1160–1250 °C

“…From Table 1 follows that parameters a and c of SS Mn 2-x Ca x Sb 2 O 7 (weberite-3T type) smoothly increase in an interval 0 Յ x Յ 1.5, and at x = 1.6 parameter a decreases, and parameter c increases. Similar change of these parameters is established in the literature [40] for a mineral of Ca 3 MnSb 4 O 14 (x = 1.5 in Table 1 [14] are at A1 (distorted cube) and A3 (polyhedron can be described as irregular bicapped octahedron) positions and Mn 2+ in A2 positions. The atoms of A2 positions are in a tetragonally distorted (2 + 4) octahedron with axial compression along [001].…”

“…[7][8][9][10] The complex antimony oxides K(Na)SbWO 6 and Bi 3 SbO 7 with a pyrochlore structure, [11,12] which are characterized by a high degree of disorder of their cation and anion sublattices, are promising ion exchangers and ionic conductors. Ionic conduction is also typical of the perovskite-like oxide Sr 0.5 CaSb 0.5 O 3-x [13,14] owing to a high level of oxygen vacancies in this compound.…”

Drastic Differences between the Local and the Average Structures of Sr2MSbO5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

“…The average crystal structures and conductivities of several A 2 BB ′O 5.5 compounds which have very large B -site cations have been reported previously. − These compounds all have ideal cubic double-perovskite average structures with space group Fm -3 m and no long-range ordering of the oxygen vacancies. They also share a tendency to absorb water to form hydrated compounds.…”

“…5 The average structure and conductivity properties of the related compound SrCa 2 SbO 5.5 have been reported recently as well. 6 There are also compounds in which Sb 5+ has been replaced by Nb 5+ or Ta 5+ , such as Sr 3 NbO 5.5 and Sr 3 TaO 5.5 . 7−9 These compounds have been observed to conduct protons under wet conditions.…”

Effect of Structural Modification by MnO2Addition on the Electrical Properties of Lead Free Flux Grown (Na0.5Bi0.5)TiO3–(K0.5Bi0.5)TiO3Single Crystals

“…The activation energy values corresponding to oxygen vacancies are on the order of 0.2−0.4 eV. 30,31 The E a values in the range 0.035−0.040 eV suggested a low oxygen vacancy migration at low and intermediate temperature in Mnmodified crystal and confirmed their contribution at high temperature. But reduction of oxygen vacancies will be more pronounced in the case of Mn 2+ valence facilitating the movement of ferroelectric domains.…”